Gut microbiota cannot compensate the impact of (quasi) aposymbiosis in Blattella germanica

The German cockroach Blattella germanica is a good model to study complex symbiotic relationships because two symbiotic systems coexist in a single individual: the endosymbiont Blattabacterium (living inside specialized cells called bacteriocytes) and the gut microbiota. Whereas the role of the endosymbiont has been fully elucidated, the function of the gut microbiota remains unclear. Its study will benefit from the availability of insects deprived of Blattabacterium. Our goal is to determine the effect of the removal (or, at least, reduction) of the endosymbiont population on the cockroach's fitness under a normal gut microbiota community. For this purpose, we treated our cockroach population with rifampicin to decrease the amount of endosymbiont in the following generation. As the treatment also affects rifampicin-sensitive gut bacteria, we allowed it to recover for at least 20 days before sampling. We found that after this antibiotic treatment, the endosymbiont population remained extremely reduced and only the microbiota was able to recover, although it could not compensate for the endosymbiont role, and host's fitness was drastically affected. This accomplished reduction, however, is not homogenous and requires further study to develop stable quasi-aposymbiotic cockroaches.